1. Field of the Invention
The present invention generally relates to a DSL communication method and a DSL communication device and, more particularly, to a DSL communication method which interconnects a user and a center by using a 2-wire telephone line and a DSL (Digital Subscriber Lines) communications technology so that the user and the center intercommunicate, and to a DSL communication device adopting the DSL communication method.
2. Description of the Related Art
In an intercommunication according to an xDSL communications technology, such as HDSL (High-bit-rate DSL), SDSL (Symmetric DSL), ADSL (Asymmetric DSL), and VDSL (Very-high-bit-rate DSL) using a 2-wire telephone line, it is difficult to maintain a constant communication quality because a line quality fluctuates due to mutual interferences with a conventionally existing communications technology (telephone, an analog modem communication, an ISDN, etc.) in a frequency band.
Thereupon, for the purpose of adapting to circumstances where a constant communication quality cannot be maintained, the ITU-T recommendations “G.992.1 (G.dmt): Appendix 2” and “G.997.1 (G.ploam)”, which are international standards, propose concepts of a method for maintaining an optimal communication quality under constantly changing circumstances by providing a countermeasure named “Dynamic Rate Adaptation” realizable during an online intercommunication against line quality fluctuations.
However, the above-mentioned method requires supports from intercommunicating DSL devices, such as a negotiation between intercommunicating DSL devices, or an exchange of line quality information therebetween. The method functions only when these method supports are in synchronization. Further, the method can be said to be an optional function.
As described above, an intercommunication according to an xDSL communications technology is performed with a constantly fluctuating line quality, which requires an addition of an optional function for maintaining an optimal communication quality under such circumstances. This addition makes DSL devices functionally complicated, and increases apparatus costs. Also, this addition necessitates integrated functions in operating a system including those DSL devices. This raises a problem in interconnecting DSL devices of different vendors at user/center sides.